Canadian study finds flu vaccine working well against H1N1

Canadian researchers today released a preliminary estimate that this year's influenza vaccine reduces the risk of infection from the 2009 pandemic H1N1 (pH1N1) virus by 74%—apparent good news in a season when that strain is by far the most common one in North America.

Writing in Eurosurveillance, the researchers also said the pH1N1 virus has changed little since it emerged nearly 5 years ago. That means the strain in the vaccine remains well matched to the circulating virus, and it should allay concern that evolution of the virus may account for its predominance this winter, they say.

"Our interim findings indicate that the 2013/14 TIV [trivalent influenza vaccine] provides substantial protection against resurgent but conserved A(H1N1)pdm09 viruses circulating in Canada during the 2013/14 season, reducing the risk of medically-attended laboratory-confirmed A(H1N1)pdm09 illness by about three quarters," says the report by Danuta Skowronski, MD, of the British Columbia Centre for Disease Control, and colleagues.

A more typical level of effectiveness for seasonal flu vaccines is around 60%. For example, a midseason analysis by the US Centers for Disease Control and Prevention in January 2013 found that the seasonal vaccine then was about 62% effective. Also, a careful meta-analysis of flu vaccine effectiveness (VE) studies published by researchers at the University of Minnesota's Center for Infectious Disease Research and Policy, publisher of CIDRAP News, in 2011 found that flu vaccines yielded about 59% protection in working-age adults.

The Canadian authors caution that their estimate is preliminary, based on only part of the season, and may change by its end.

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